1. Field of the Invention
This invention relates to the construction and use of bifilar absorbers as applied to helicopter rotors.
2. Description of the Prior Art
Prior to this invention bifilar absorbers as used on helicopter rotors have operated at approximately .+-. 30.degree. amplitude at design forward speed. To prevent undertuning at any speed up to design forward speed the bifilar absorbers have been overtuned by increasing the tuning pin diameters. This results in dissimilar pendulum motions which produce rotating system vibratory excitations at twice the tuned frequency of the bifilar at all flight conditions except the design forward speed at which all of the masses of the bifilars reach an amplitude at which overtuning no longer exists. Due to dissimilar motions of the several absorbers on the rotor, these excitations will excite the fixed system, including the fuselage, at a frequency of 2w.sub.n -1, where w.sub.n = the tuned frequency of the bifilar absorber at the design forward speed.
U.S. Pat. No. 3,540,809, issued to W. Paul et al, illustrates a prior art installation of bifilar absorbers on helicopter rotors. The present invention is directed to improvements in such installations.